The present invention disclosed herein relates to a long shaft bit with a vibration suppressing structure, and more particularly, to a long shaft bit for cutting process, which can obtain a processed surface with good surface roughness by preventing resonance and vibration during the cutting process and thus preventing a flaw from occurring on the processed surface of a cutting subject, using a vibration suppressing structure in which a vibration absorbing body is stacked on the shank in a multi-layer and a hollow wire rod is spirally coiled in each layer of the vibration absorbing body.
Generally, a bit with a long shank is being used to perform cutting operation on the inner diameter of a cutting subject such as a cylindrical body with a deep cutting depth, e.g., a parabolic aspherical reflector. A typical bit includes a tip fixing part, a connection part, and a shaft part, which are sequentially connected to one another to form a cylindrical body. Also, a tip is mounted on one side of the front end of the tip fixing part.
When viewed from the top, the tip has a substantially rhombic shape. One of cutting edges formed at two angular parts opposite to each other is slightly protruded from the front end and the outer circumferential surface of the front portion of the edge, and is detachably mounted on the front portion of the edge.
Also, a chip pocket is formed in the tip fixing part, and is opened to the front end and the outer circumferential surface of the bit. The chip pocket includes a flat face forming a substantially one surface with a tip face, and an inclination surface that inclines toward the upper outer circumferential surface of the tip fixing part as it goes from the rear end of the face to the rear side of the tip fixing part.
The bit with the above-mentioned configuration is used to perform cutting operation on the inner diameter of a cutting subject, that is, the inner diameter of a hole that is preformed in the cutting subject. First, while a shank is mounted on a tool grip part of a machine tool such as a tailstock of a lathe via a holder, the cutting subject is mounted on a workpiece grip part of the machine tool such that the shaft line of the inner diameter of the cutting subject faces the direction parallel to the shaft line of the shank.
The cutting process on the inner diameter of the cutting subject is performed by inserting the tip fixing part and the connection part into the hole of the cutting subject and cutting the hole of the cutting subject with the cutting edge of the tip to enlarge the diameter to a predetermined dimension while rotating the cutting subject around the shaft line of the inner diameter part and generating a relative motion around the shaft line direction between the tool grip part of the machine tool and the workpiece grip part.
In the typical bit in which the cutting process on the surface of the inner diameter of the cutting subject is performed by the above-mentioned structure, since the shank is formed in a longitudinal shaft, the vibration of the machine tool generated during the cutting process is delivered to the shank, and resonance may occur between the cutting subject and the tool, causing a flaw such as a processing pattern on the processed surface of the cutting subject.
Thus, in case of a product with a surface requiring a super-precision processing like mirror surface, it is difficult to finish the product by the cutting process. Although the cutting process may be performed, the productivity or the work efficiency is significantly reduced.
As a related art, Korean Utility Model No. 20-0317304 discloses a vibration knurling bit shank. The vibration knurling bit shank including a shank fixed to a tool post to process a workpiece and a cutting tip for processing the workpiece further comprises a seating part in which the cutting tip is coupled to an upper front end of the shank by a fixing bolt, a through hole formed to be spaced from a lower part of the seating part by a predetermined distance, a fastening part cut by a predetermined width in a diagonal direction to the front lower side of the through hole, a bolt receiving part formed in an orthogonal direction to the fastening part and allowing an adjustment bolt to be inserted and coupled, and a washer having a smaller size than the predetermined width of the fastening part.
Accordingly, in the related art, a separate knurlete is not needed to form a protrusion such as a knurling on a rolling roll. However, due to the vibration by the long shaft shank, the vibration knurling bit shank is not suitable for cutting process on the inner diameter of a hole of a cutting subject. Rather, the generated vibration causes a pattern on the surface of the inner diameter, or resonance occurs.